Ni-Al2O3 nano-composite coating was prepared on the ASP30 powder metallurgical steel surface for semiconductor encapsulation mould by using electrodeposition method. Effects of Al2O3 contents on microstructure, microhardness and wear resistance of composite coating were analyzed. Results demonstrate that due to refined crystalline strengthening, dispersion strengthening and high-density dislocation strengthening of Al2O3 nanoparticles in uniform distribution, Ni-Al2O3 nano-composite coating has more compact structure and smaller grain size compared to the pure Ni coating, which are conducive to increase microhardness and wear resistance of the coating significantly. Neither too low nor too high Al2O3 contents is beneficial to improve microhardness and wear resistance of composite coating. The pure Ni coating has serious adhesion wearing, while the nano-composite coating with the moderate Al2O3 content has the best performance and it mainly has mild abrasive wear, accompanied with some adhesion wearing. Relatively serious adhesion wearing occurs on the wear surface of pure Ni coating. Differently, wearing surface of Ni-Al2O3 nano-composite coating is mainly dominated by mild abrasive wear, accompanied with some adhesion wearing. Neither too low and too high Al2O3 content is conducive to improve microhardness and wear resistance of composite coating.